1. Field of the Invention
The present invention is generally related to a spacer, and more particularly to a feed spacer for spiral-wound membrane module.
2. Description of the Prior Art
Membrane filtration procedures are well applied in industries. Therefore, various filtration membrane apparatus are designed and manufactured. For example, spiral wound membrane module is used in cross-flow filtration, and the advantages of spiral wound membrane module are smaller size, greater filtration area, and higher shear rate. A cross-sectional view of a conventional spiral wound membrane module is shown in FIG. 1, wherein the spiral wound membrane module comprises an outer cover 110, feed spacer 120, permeate spacer 130 and permeate collection tube. Besides, arrows 150 indicate the flow direction of permeate. The filtration membranes are in planar contact with the outer surface and the inner surface of the feed spacer. Furthermore, the feed spacer serves both as mechanical stabilizer for channel geometry and turbulence promoters for reducing polarization phenomena near the membrane surface.
The conventional spacer has a plurality of rows of elongated filaments, for example two rows. The filaments of a same row are substantially parallel to each other. The rows are disposed in layers where the filaments of one row are attached to, typically by fusion, and generally crossing the filaments of adjacent rows at an angle. However, no any effort has been placed on the effects of curvature of the spacer and membrane permeability in the spiral-wound modules on the pressure drop, shear rate and separation efficiency through the curved module. In conventional system, the curved spacer in a spiral wound module causes unequal shear rate at inner and outer membrane surfaces. Such unequal shear rates at the inner and outer surfaces would be expected to have an adverse impact on the membrane module performance because of different fouling characteristics for adjacent membrane leaves. Therefore, there is still a need to develop new feed spacer for spiral-wound membrane module, so as to balance the shear rate of inner and outer surfaces of the feed spacer, and then to prolong the service life of spiral-wound membrane module.